In U.S. Pat. No. 4,583,888 of Yoshikatsu Mori et al., a drill bit is disclosed which is made of cemented carbide. As brought out in that patent, the quality of chip ejection of the drill bit design influences the cutting resistance and, thus, it is considered very important to provide improved chip ejecting ability of such drill bits. As shown in the Mori et al. patent, the drill bit defines a conical tip and a pair of diametrically opposite flutes. The patent teaches a preselected distance between the cutting lip and the flute wall of the drill bit tip to promote chip ejection. As shown, the cutting lip extends across the distal end of the flute. The patent discloses, as prior art, such cutting edges having a generally rectilinear configuration, and the cutting edge of the Mori et al. tool is disclosed as a continuous arcuate edge.
Such conventional drill bit constructions have a serious disadvantage in the forming of relatively large chips from the metal being worked during the drilling operation. These chips tend to interfere with subsequent cutting action, reducing the quality and efficiency of the hole drilling operation.
It is further known to provide, in such drill bit tips, diametrically extending inserts defining the cutting edge. Such inserts are conventionally secured in a slot extending across the drill tip by suitable brazing, or the like. Thus, the cutting edge may be defined by a portion of the drill bit formed of a material differing from the material forming the body of the drill bit.
It is further conventional, in such drill bits, to provide coolant passages extending longitudinally through the body of the bit and opening through the conical tip surface. The coolant lubricates the work during the machining operation and, at the same time, acts to remove the chips previously cut from the work. As discussed above, the prior art structures present a serious problem in the incomplete and inefficient removal of such chips, thereby placing a highly undesirable limitation on the efficiency and speed of such drilling operations. Further, the failure to efficiently remove the chips shortens the useful life of the drill bit by the reengagement of the chips with the cutting edge.